In a variety of scientific, industrial, and medically related applications, it can be desirable to transfer energy or power across some type of boundary. For example, one or more devices that require power can be located within the confines of a fully sealed or contained system in which it can be difficult and/or undesirable to include a substantial and/or long term source of power. It can also be undesirable to repeatedly enter the closed system for a variety of reasons. In these cases, a power source external to the fully sealed or contained system and some feasible means of transferring power from the external source to one or more internal devices without direct electrical conduction can be preferable.
One example of a closed system is the human body. In several medically related and scientific applications, a variety of prosthetic and other devices that require power can be surgically implanted within various portions of the body. Examples of such devices include a synthetic replacement heart, a circulatory blood pump or ventricular assist device (VAD), a cochlear implant, a pacemaker, and the like. With respect to the human body, complications associated with repeated surgical entry make replaceable internal power sources impractical. Likewise, the risk of infection and/or dislodgment make direct electrical linkages between external power supplies and implanted devices undesirable.
Accordingly, transcutaneous energy transfer (TET) systems are employed to transfer energy from outside the body to inside the body in order to provide power to one or more implanted devices from an external power source. TET systems use an inductive link to transfer power without puncturing the skin. Thus, the possibility of infection is reduced while comfort and convenience for patients is increased.
TET devices typically include an external primary coil and an implanted secondary coil that are separated by intervening layers of tissue. The primary coil is designed to induce alternating current in the subcutaneously placed secondary coil, typically for transformation to direct current to power an implanted device. TET devices therefore also typically include electrical circuits for periodically providing appropriate alternating current to the primary coil. These circuits typically receive their power from an external power source.
As implanted medical devices have become increasingly complex, a need has developed to also provide data communication between the implanted devices and an outside operator, such as a physician or scientist. As with the transfer of power, it can be desirable to provide a method of communication that does not require a physical connection, e.g., wires passing through the skin, between the implanted device and external monitors or controllers.
Radio frequency (RF) communication systems have been developed to address the need for bi-directional data communication between operators and/or patients and implanted medical devices. These systems are components of the implanted system and use a separate RF antenna so that an external controller or programmer can communicate with internal sensors or control elements. Typically, the separate RF antenna is implanted in a patient away from the implanted secondary TET coil to avoid radio interference when the coil is in use.
Prior art RF antennas have several disadvantages. First, they suffer from signal attenuation. RF antennas are often implanted deeper within a patient's body than the secondary TET coil, for example, within the chest or in the abdominal cavity. Placing the RF antenna in such a location requires communicating through a large amount of muscle, skin, and fat, resulting in a large amount of signal attenuation during use.
Second, the use of a separate RF communication antenna means there is yet another component that must be implanted into a patient's body and connected to an implanted device controller or other implanted circuitry. Having this additional component increases the complexity of the system, requires a more invasive surgery to implant, and provides another possible point of failure in the system.
Thus, a need exists for a better performing and more integrated RF antenna for use in a TET system.